1. Field of the Invention
The present invention relates to a well string shock absorber wherein an inner member and an outer housing form a telescopic structure with resilient means engageable between the body and housing to cushion telescopic contraction and extension of the inner body and outer housing in response to loads and vibrations encountered during drilling.
2. Description of the Prior Art
Various types of drill string shock absorbers have been provided in the past and are currently in use. As the drill bit which is connected to the drill string is rotated to cause penetration of the bit through the earth formation, the bit may tend to jump off the bottom of the hole being drilled which imparts shock loads to the drill string and also may result in reduced penetration rate of the bit and drill string through the formation. Drilling fluid is circulated downwardly through the drill string and through the bit for a number of reasons including carrying cuttings from the bottom of the well bore to the earth's surface.
Heretofore, it has been recognized that shock absorbing mechanisms are responsive to the pump pressure acting to move the drilling fluid down to the bottom of the well bore and back up to the earth's surface. For example, see U.S. Letters Pat. Nos. 4,186,569 and 4,194,582 issued on Feb. 5, 1979 and Mar. 25, 1980, respectively. More particularly, the drilling fluid pressure acting on the lower end of the inner body of prior art telescopic shock absorber structures tends to urge the inner body upwardly relative to the outer housing. In some circumstances, this can be extremely undesirable in that the pressure may be sufficient to fully extend the outer housing and inner body and the telescopic structure is thus rigid unless the weight of the drill string is sufficient to overcome the hydraulic force tending to extend the inner body and outer housing of the telescopic structure to their extreme limits.
For various reasons it is undesirable to have a shock absorbing tool in a drill string which cannot function independently of the pump pressure, or of the pressure of the drilling fluid passing through the telescopic structure since the operating range of the shock absorber may be limited, and may not operate effectively and properly under all conditions as desired.
Further, prior art shock absorbers provide stop shoulder means which limits the extension and contraction of the inner body and outer housing forming the telescopic structure, and such stop shoulder means generally have either one or both of such stop shoulder means arranged on the telescopic structure in the liquid receiving chamber in which the spring means or resilient means is provided.
Quite often in drilling a well bore a drilling jar is employed in the drill string to impart a jar impact up and/or down as may be desired from time to time in the event that the drill string becomes stuck. The prior art positions one or more of the shoulder stop means in the chamber in which the resilient or spring means is provided along with liquid, and such structure may cause substantial forces to be imparted to the shock absorber mechanism when the drilling jar is actuated which may damage if not completely destroy the shock absorber mechanism.
Also, the prior art provides restricted passages to dampen the loads and vibrations and to dampen the relative movement between the shock absorber components. However, this continuous dampening ability substantially prevents deactivation of prior art devices when drilling jar loads or impacts are applied thereto which may damage the shock absorber components.
While Belleville springs have been employed as the resilient means in shock absorber tools, they have not been structured to trap liquid therein as they are compressed to provide additional load carrying ability.